In an unprecedented step, the under-fire head of North Wales Police released images showing Mr Shaw, a 71-year-old retired bank manager, speeding through Acrefair, near Llangollen.

Mr Brunstrom claimed the video evidence proved Mr Shaw was not overtaking a tractor - as he claimed in court and to the Daily Post - but was driving dangerously.

And he said Mr Shaw's statements were "outrageous and a complete perversion of the truth".

But as the war of words intensified Mr Shaw hit back.

He stormed: "This is the last desperate throw of a man who is seriously rattled because someone has complained about him at last."

Mr Brunstrom said he did not usually respond to such complaints but said on this occasion he "could not let go".

"I am particularly irritated by Mr Shaw personally because he has made statements which I don't think are true," he said.

"He has directly accused us of an obvious blatant example of police malpractice and he asked the court when he pleaded guilty to the offence to issue a reprimand against the police for our activity.

"This is ridiculous. This person is properly convicted but claims he is a law abiding citizen. In fact, he is not. He is not an honest law abiding pensioner with a blemish-free record - he is a convicted speeding motorist.

"He has no leg to stand on. He has simply chosen to break the law."

The video, taken by an Arrive Alive van in November last year, shows Mr Shaw driving at 39mph in a 30mph zone. Eight more cars - some with headlights and windscreen wipers on - pass the van before a tractor passes over two minutes later.

Mr Brunstrom said: "Mr Shaw alleges he was concluding a manoeuvre to overtake a slow-moving tractor. That is just not true.

"He may well have overtaken a tractor but that does not begin to provide, as you can see from the evidence, any resemblance of an excuse. He is driving dangerously.

"This is not police malpractice. On the contrary, this is professional police work of the highest calibre. We are determined to save lives."

He added: "A pensioner driving a motor vehicle at 40mph is just as dangerous as an 18-year-old driving at 40mph. If a pedestrian is hit by a car travelling at 40mph they are very likely to die. At 30mph there is a 50-50 chance of surviving.

"Straying a few mph over the limit kills people. At the speed he was driving had he hit a pedestrian he would have killed them."

Two years ago a pedestrian was killed on the stretch of road where Mr Shaw was caught speeding.

Mr Brunstrom said: "The reason we are there is because there was a fatal road traffic collision when a pedestrian was run over and killed.

"We had a police officer sitting in a van, deliberately sitting there because it is a dangerous location, taking moving pictures of the traffic.

"I want to make a very principled stand that if you chose to break the speed limit in a dangerous fashion you are risking the lives of others and you will be caught and prosecuted.

"Thirty-nine mph appears to Mr Shaw to be something which happens to law abiding folk who unintentionally find themse lves in a breach of the regulations. "I want to challenge that - it is just not right. We were there because someone died at the location and we have managed to reduce casualties at this location."

Mr Brunstrom said "there was no evidence" the car involved in the fatal accident "was exceeding the speed limit".

But he added there had been "a very significant reduction in the number of casualties at that site" since Arrive Alive started in 2001.

In 1999 there were 33 casualties, in 2000, 30 casualties, in 2001, 20 and in 2002, 21. Mr Brunstrom said: "What we would like is people not to break the law. If you don't break the law the police cannot get their 'pound of flesh' because we cannot prosecute you.

"The answer for Mr Shaw is not to complain about it but to keep his right foot off the accelerator pedal, to pay more attention to his speed, to drive more slowly, more safely, and not to complain afterwards the nasty horrible police have caught him out.

"Yes, we get our money back which makes it easier to catch people, but we would much rather not have to give out any fixed penalties at all.

"We don't want to prosecute people. We want them to drive more slowly and more safely."

But Mr Shaw, who pleaded guilty to speeding before Mold magistrates, last night insisted his driving was safe.

He said: "The evidence is completely wrong.

"The tractor started to turn left as I overtook it, but I don't know if it completed the move. It may have just pulled over to let the traffic past.

"That is why the tractor is so far behind me. It is either a different tractor or it stopped. I was completing the overtaking manoeuvre when I was caught speeding.

"I do not deny I was doing 39mph.

If the speed camera says I was then I must have been. But I had been over-taking, and there was at least one other car following me, so I did not start to slow down until I was well past the tractor."

And he said he was "shocked" Mr Brunstrom had gone to such lengths to defend himself.

He said: "He is irritated because I have complained about his conduct. That is why he is getting upset. And I am delighted to hear he is.

"I would have thought he had better things to do. He has some of the highest conviction rates for motoring offences in the whole country and some of the lowest for convicting criminals.

"The law is for catching criminals - that is what he should be doing."

Mr Brunstrom said the right time to address "crime management" was at tomorrow's North Wales Police Authority meeting.

He said: "I am very disappointed by Mr Shaw's attitude. I expect a very great deal more responsibility from a 71-year-old retired bank manager.

"I do not expect people like him to be deliberately breaking the law and misleading the public about it afterwards.